An arrangement of threaded spindle and spindle nut in the piercing cross-bar for limitation of the mandrel stroke is known for example from British Pat. No. 929,056. Here the mandrel stroke-limiting rods are fixed at one end in the cylinder cross-head and carry stops at their other end, opposite the counter platen. The piercing cross-bar is supported against these stops by their one stroke and thereby by that of the mandrel-limiting threaded nut, which is adjustable by means of a threaded spindle.
Further, another arrangement is known from U.S. Pat. No. 3,391,566, in which the stroke of the mandrel stroke-limiting rods is adjustable by means of threads on the rods and a threaded nut arranged in the piercing cross-bar, and the mandrel stroke-limiting rods, with an abutment located at their free end, come up against a stop device, in the cylinder cross head. Also in this case there is provided a hydraulic piercing device, consisting of cylinder and piston, in the main press piston of the press.
The constructional expense for the provision of threaded spindles, spindle nuts and a central drive system is relatively large. Furthermore, in extruding over the mandrel which is fixed in the opening of the die, the opposing pressure which arises towards the end of the extrusion process on the annular surface of the mandrel tip, due to the difference in cross-sectional areas of the mandrel and the undercut mandrel tip, must be taken up through the piercing piston and piercing cylinder from the main press piston. The force thereby created in the piercing cylinder by the opposing pressure is therefore subtracted from the pressing force.